Isolator switches provided with grounding switch blades and ground responsive signalling and protective means

ABSTRACT

A metal-clad isolator switch for multiple interruption divided in two parts insulated from each other and comprising means for connecting the interconnected movable switching contacts of the isolator switch with earth and a selectively operating signalling and protecting system which selectively indicates, when and in which one of the isolator switch parts an unwanted earthconnection occurs.

United States Patent 72] Inventors Rintje BoersmaJlar-melen [56] References Cited Gijsbert W. lrik, Bilthoven, both of UNITED STATES PATENTS Netherlands 80 O0 6 4 8// 1772% Ill m m mT m ."m m m mT l n n A m.mmm u Tm ah e .m o RFRMBR O 6779 56666 99999 HUN 22522 00 800 35 97 w 23365 43258 ,33 23333 O' f M 8 fiMu LU 8 AN a de mm I 8 P e...- Pkmw AFPA .111] I253 2247 [32] Priority Aug. 4, 1969 Netherlands [3 l 691 1833 m F m w & m

r e wo i m mx m H mm mm S MA [54] ISOLATOR SWITCHES PROVIDED WITH Attomey-Snyder and Butrum GROUNDING SWITCH BLADES AND GROUND RESPONSIVE SIGNALLING AND PROTECTIVE MEANS lo chims'a Drawing Figs ABSTRACT: A metal-clad isolator switch for multiple interruption divided in two parts insulated from each other and comprising means for connecting the interconnected movable switching contacts of the isolator switch with earth and a selectively operating signalling and protecting system which selectively indicates, when and in which one of the isolator switch parts an unwanted earth-connection occurs.

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lllllllli. lun n n PATENTEDAUGI 0m 3; 599 0 1 sum 1 or 2 Fl G. 1 INVENTORS iuTJ'E- soERsMA GJ'JSBERT IRFK M, -L MAJ ATTOR NEYS SHEET 2 BF 2 PATENTEU AUG 10 1971 GIJSBERT w. IRiK ATTORNEYS ISOLATOR SWITCHES PROVIDED WITH GROUNDING SWITCH BLADES AND GROUND RESPONSIVE SIGNALLING AND PROTECTIVE MEANS The invention relates to a metal-clad isolator switch for high voltage and multiple interruption, comprising a metal envelope which is insulated from earth and connected with earth via a signalling and protecting circuit only, said envelope containing two spaced fixed contacts and two movable switching contacts mounted for cooperation with said fixed contacts in the space left between the latter, said fixed and said movable contacts being insulated from the envelope, said movable switching contacts being, at least in the closed condition of the isolator switch, electrically conductively interconnected and being supported by an insulator attached to the envelope and dividing the space within the envelope into two switching chambers which are separated by said insulator in a gastight manner and each contain a fixed contact and a movable switching contact, and a device for earthing the movable switching contacts, when the isolator switch is in its open condition.

An isolator switch of this construction is the subject matter of copending application Ser. No. 867,745, filed Oct. 20, 1969. The invention has the object to improve this formerly constructed switch in such a manner that, should an earthconnection occur, it will indicate in a simple way, in which one of the two switching chambers said earth-connection has occurred. The invention consists in that the portion of the envelope which each surround a switching chamber are also insulated from one another and are each connected with earth by an individual conductor cooperating with the signalling and protecting circuit, the movable switching contacts being coupled with the signalling and protecting circuit in the open condition of the isolator switch and said circuit being arranged, in such a manner, that at the occurrence of an earth-connection in the isolator switch it is indica ed, in which one of the two switching chambers the earth-connection occurs.

The isolator switch may for obtaining the desired selective signalling and protection be constructed, in such a manner, that each movable switching contact cooperates with an individual earthing-switch and with an individual part of the signalling and protecting device, the movable switching contacts being interconnected by an auxiliary switch which is closed in the closed condition of the isolator switch and open in the open condition of the isolator switch. in this case two separate signalling and protecting circuits are used. If in this construction an isolator switch having axially movable coaxial switching rods mounted for movement in opposite directions is used, said switching rods may each be mounted in and electrically conductively connected with an individual metal tubular member which is contained in and supported by the insulator, said tubular members being spaced and insulated from one another and a slide contact may be provided in the tubular members which is operated by a switching rod, said slide contact constituting together with said tubular members the auxiliary switch and establishing, in the closed condition of the isolator switch, an electrically conductive connection between said tubular members and said switching rods, but keeping, in the open condition of the isolator switch, the switching rods electrically separated from one another. The auxiliary switch is then automatically coupled, with the switching rods, so that a separate driving gear for said auxiliary switch can be dispensed with.

If the isolator switch is provided with two movable switching contacts, which are permanently electrically conductively interconnected by a conductor extending through the insulator, and with an earthing-switch cooperating with both switching contacts and found in one of the two switching chambers only, the conductor extending between the two movable switching contacts, the conductor extending between earth and the portion of the envelope surrounding the switching chamber, in

which the earthing-switch is accommodated, and the conductor extending between earth and the portion of the envelope surrounding the other switching chamber may each be coupled with an individual input-circuit reacting on the current, that flows through the relative conductor, and forming part of a composite control-circuit that is connected between said conductor and a signalling and protecting system, said control-circuit bringing said signalling and protecting system, at the event of an earthwonnection in one switching chamber, into one and, at the event of an earth-connection in the other switching chamber, into the other one of two operative conditions. A reliable isolator switch having this selective signalling and protecting circuit is obtained, when said conductors are each coupled with said input-circuit of the control-circuit via a current transformer, said control-circuit comprising two summation transformers which are each provided with two primary windings and one secondary winding, the one primary windings of said summation transformers being connected in series and fed by the current transformer coupled with the conductor interconnecting the movable switching contacts, the other primary winding of one summation transformer being fed by the current transformer coupled with the conductor extending between earth and the envelope of the switching chamber, in which the earthing-switch is accommodated, and being coupled in counterconnection with the first mentioned primary winding of said summation transformer, the other primary winding of the other summation transformer being fed by the current transformer coupled with the conductor extending between earth and the envelope of the other switching chamber and being coupled in concurrent connection with the first mentioned primary winding of said other summation transformer and the secondary windings being connected in counterconnection to a double acting signalling and protecting device.

The invention will be further elucidated with the aid of the drawing. In the drawing is:

FIG. 1 an axial sectional view of an isolator switch having a selective signalling and protecting circuit constructed in accordance with the invention;

FIG. 2 a diagrammatical view of an other isolator switch provided with a selective signalling and protecting circuit and FIG. 3 a diagrammatical view of an isolator switch shown in FIG. 2 provided with a variant of the signalling and protecting circuit.

In the drawing 1 and 2 are two tubular portions of a metal envelope which are insulated from one another and earth.

These two portions of the metal envelope are insulated from each other by means of a disc-shaped insulator 3. This insula tor supports two coaxial metal tubes 4, 5 which extend in the axis of the portions ll, 2 of the envelope. The tubes 4, 5 are insulated from each other by a space 6 and they carry each an axially movable switching rod '7, 8. These switching rods cooperate with fixed contacts 9, l0 and they are moved by means of screwed rods ll ll, M. which can be driven via the driving gear 113 by a driving shaft M. The screwed rods ll, 12 cooperate with nuts l5 l6 insulatedly mounted in the switching rods 7, 8. Furthermore, the tubes 4, 5 carry each a movable earthing-contact l7, 18 which, in the open condition of the isolator switch, are brought into cooperation with a fixed contact 19 26 respectively, which is electrically conductively connected with the envelope 1, 2 respectively. The earthing-contacts l7, 18 are driven by the switching rods 7, 8 in such a manner, which is not described, that they are forced by said switching contacts, just before the switching contacts 7, 8 reach their open position, from the inactive position shown in complete lines into the active position shown in dotted lines and are swung from the active position into the inactive position, in which position they are locked, just after the switching rods 7, 8 have left their open position. The portions 1, 2 of the envelope and also the fixed earthing contacts 19, 20 are each connected to earth via a conductor 21, 22. The conductors 21, 22 are each coupled via a current transformer 23, 24 with an individual signalling and protecting device 25, 26.

In the closed condition of the isolator switch the insulating space 6 is bridged by a slide contact 27, which is secured to a movable block 28 contained in the tube 5. This block is forced by a spring 29 in the shown position, in which the slide-contact 27 interconnects the tubes 4 and 5, and the switching rods 7 and 8 electrically conductively with each other. If the isolator switch is opened, the switching rods 7, 8 are moved towards each other and the block 28 provided with the slide-contact 27 is forced against the driving mechanism 13, so that the electrically conductive connection between the tubes 4 and is broken. The switching chambers which are spatially and electrically separated from each other by the insulator 3 are then each separately grounded. This means, that, when the switch is in the closed condition and the switching rods 7, 8 are earthed, an earth-connection, for instance between the fixed contact 9 and the envelope 1 or a rupture from the fixed contact 9 to the opened switching rod 7, produces an earthcurrent through the conductor 21, so that the signalling and protecting device 25 is set in action. Due to the separation at 6 the earth-connection or the rupture in the switching chamber surrounded by the envelope 1 does not influence the conditions in the switching chamber enclosed by the envelope 2, so that the signalling and protecting device 26 remains inoperative. However, at the event of a disturbance in the last mentioned switching chamber the signalling and protecting device 26 will be fed by the earth-current flowing through the conductor 22, whereas the device 25 remains inoperative.

In the isolator switch shown in FIG. 2 and 3 the movable switching contacts 30, 31 are permanently electrically conductively interconnected by a conductor 32. The switching contacts 30, 31 cooperate with fixed contacts 33, 34 and in the open condition of the isolator switch only the switching contact 30 is brought into contact with a fixed earthing-contact 35. The portions 1 and 2 of the envelope which are insulated from each other by the insulator 3 are each connected to earth via a conductor 21, 22 forming part of the current transformer 23, 24. The conductor 32 is surrounded by the secondary winding 36 of a third current transformer.

The circuit for the selective signalling and protection shown in FIG. 2 comprises two summation transformers 37, 38 which are each provided with two primary windings 39, 40 and 41, 42 andone secondary winding 43, 44. The primary winding 39, 41 is connected to the current transformer 23, 24 respectively. The primary windings 40 and 42 are connected in series and fed by the current transformer 36. The windings 39 and 40 are coupled concurrently and the windings 41 and 42 are coupled in counterconnection in respect of the summation transformers 37, 38. The secondary windings 43, 44 of the summation transformers 37, 38 feed together a double acting relay 45 which is provided with two oppositely operating coils 46, 47. This relay is adapted to close by means of a contact 48 the circuit of a signalling and protecting device 49, when the coil 46 is fed by the transformer winding 43, and adapted to close by means of a contact 50 the circuit of a signalling and protecting device 51, when the coil 47 is fed by the transformer winding 44. This device operates as follows:

If the isolator switch is in its closed condition, the conductor 32 is able to lead current, so that via the current transformer 36 a current can flow through the primary transformer windings 40, 42. Both coils 46, 47 of the relay 45 are then excited, so that the relay is held in the condition of rest and the devices 49, 51 remain inactive. In the open condition of the isolator switch the envelope 1 is grounded via the conductor 21 whereas the switching contacts 30, 31 the conductor 32 and the envelope 2 are grounded via the conductor 22. Should an earth-connection occur between the fixed contact 34 and the envelope 1, the earth-current will flow through the conductor 21 and only the coil 46 of the relay 45 will be fed by the transformer 37, so that the contact 48 is closed and the signalling and protecting device 49 is set in action. Should the insulating space between the fixed contact 34 and the switching contact 31 be ruptured, a current will flow through the conductors 32 and 22. This results in that the primary windings 40 and 42 will be fed by the current transformer 36 and the primary winding 41 will receive current from the current transformer 24. Since the windings 41 and 42 oppose each other the transformer 38 remains inactive, so that the coil 47 of the relay remains currentless. However, a voltage is induced in the secondary winding 43 by the primary winding 40, so that the coil 46 of the relay 45 is fed, the contact 48 is closed and the signalling and protecting device 49 is brought into operation. Also in this case the disturbance occurring within the envelope 1 is indicated by the device 49. However,

if an earth-connection should occur between the fixed contact 33 and the envelope 2 or if a rupture should occur between said fixed contact and the switching contact 30, an earth-current will flow through the conductor 22, so that only primary winding 41 of the transformer 38 will be fed. Thereby the coil 47 of the relay 45 is excited via the secondary winding 44, so that the contact 50 is closed and the signalling and protecting device 51 is set in action. consequently, also in this apparatus it is indicated, in which one of both switching chambers a disturbance occurs. In the circuit illustrated in FIG. 3 the summation transformers 37, 38 and the double acting relay 45 of the circuit shown in FIG. 2 are replaced by three relays 52, 53, 54. The relay 52 is fed by the current transformer 23, the relay 53 is flow by the current transformer 36 and the relay 54 is fed by the current transfonner to If the relay 52 is brought into operation the contact 55 is closed. If the relay 53 is fed the contact 56 is-opened and the contact 57 is closed and if the relay 54 becomes operative the contacts 58 and 59 are closed. This device operates as follows:

At the event of an earth-connection between the fixed isolator switch contact 34 and the envelope 1 the earth-current will flow through the conductor 21, so that only the relay 52 will be fed and the circuit of the signalling and protecting device 49 will be closed by the contact 55. Should a rupture occur between the fixed contact 34 and the switching contact 31, an earth-current will flow through the conductor 32 and the conductor 22, so that the relays 53 and 54 will be fed by the current transformers 36 and 24. This has the effect that the circuit of the signalling and protecting device 49 is closed by the then closed contacts 57 and 59 which are connected in series. The signalling and protecting device 51 remains inactive, as

' the contact 56 is then opened. If the earth-connection or the rupture should occur in the switching chamber surrounded by the envelope 2, the earth-current will only flow through the conductor 22, so that only the relay 54 will be excited and the circuit of the signalling and protecting device 51 will be closed by the contact 53. The device 49 remains inactive, since the contacts 55 and 57 then remain open. If the isolator switch is closed and the service current flows through the conductor 32, only the relay 53 is fed by the current transformer 36, so that the contact 56 is opened and the contact 57 is closed. The relays 52 and 54 then remain in their position of rest, so that the contacts 55, 58 and 59 remain open and no one of the two signalling and protecting devices 49 and 51 will be set in action.

What we claim is:

I. A metal-clad isolator switch for high voltage and multiple interruption, comprising a metal envelope which is insulated from earth, a selectively operating signalling and protecting system connected between said envelope and earth, two'.

spaced fixed contacts, two movable switching contacts mounted for cooperation with said fixed contacts in the space left between the latter and being, at least in the closed condition of the isolator switch, electrically conductively interconnected, said fixed contacts and said movable contacts being insulated from the envelope, an insulator attached to the en'- velope and supporting said movable switching contacts, said insulator dividing the space inside the envelope into two switching chambers, which are separated in a gastight manner by said insulator and each contain a fixed contact and a movable switching contact, means for connecting the movable switching contacts with the envelope, when the isolator switch is in its open condition, the envelope portion surrounding one switching chamber being insulated from the envelope portion surrounding the other switching chamber, a conductor extending between one envelope portion and earth and a conductor extending between the other envelope and earth said conductors operatively coupling said envelope portions and, when the isolator switch is in its open condition, the movable switching contacts with the signalling and protecting system in a selective manner, so that at the event of an earth-connection in the isolator switch the selectively operating signalling and protecting system indicates, in which one of the two switching chambers said earth-connection occurs, two individual earthing-switches, each one thereof cooperating with a movable switching contact to connect the latter with the relative envelope portion, two individual signalling and protecting circuits constituting together the selectively operating signalling and protecting system and an auxiliary switch inserted between the movable switching contacts and being closed to interconnect said switching contacts, when the isolator switch is in its closed condition, and being open to separate the switching contacts, when the isolator switch is in its open condition,

2. A metal-clad isolator switch as claimed in claim 1, in which the movable switching contacts are in the form of axially movable coaxial switching rods mounted for movement in opposite directions and two insulatedly spaced metal tubular members supported by the insulator are provided, each switching rod extending in and being electrically conductively connected with a tubular member, and in which a slide contact is provided which cooperates with the tubular members and is operated by one of the switching rods, said tubular members and said slide contact constituting together the auxiliary switch.

3. A metal-clad isolator switch for high voltage and multiple interruption, comprising a metal envelope which is insulated from earth, a selectively operating signalling and protecting system connected between said envelope and earth, two spaced fixed contacts, two movable switching contacts mounted for cooperation with said fixed contacts in the space left between the latter and being, at least in the closed condition of the isolator switch, electrically conductively interconnected, said fixed contacts and said movable contacts being insulated from the envelope, an insulator attached to the envelope and supporting said movable switching contacts, said insulator dividing the space inside the envelope into two switching chambers, which are separated in a gastight manner by said insulator and each contain a fixed contact and a movable switching contact, means for connecting the movable switching contacts with the envelope, when the isolator switch is in its open condition, the envelope portion surrounding one switching chamber being insulated from the envelope portion surrounding the other switching chamber, a conductor extending between one envelope portion and earth and a conductor extending between the other envelope and earth said conductors operatively coupling said envelope portions and, when the isolator switch is in its open condition, the movable switching contacts with the signalling and protecting system in a selective manner, so that at the event of an earth-connection in the isolator switch the selectively operating signalling and protecting system indicates, in which one of the two switching chambers said earth-connection occurs, a conductor extending through the insulator and permanently conductively interconnecting the two movable switching contacts, an earthingswitch cooperating with both switching contacts in one of the two switching chambers only, and a composite control-circuit including three individual input-circuits forming part of said control-circuit and two individual signalling and protecting devices controlled by said control-circuit, the conductor interconnecting the two movable switching contacts, the conductor extending between earth and the envelope portion surrounding the switching chamber in which the earthing-switch is accommodated, and the conductor extending between earth and the envelope portion surrounding the other switching chamber each being operatively coupled with an individual input-circuit, said input-circuit reacting on the current that flows through the relative one of said conductors and said control-circuit bringing, at the event of an earth-connection in one switching chamber, one signalling and protecting device and, at the event of an earth-connection in the other switching chamber, the other signalling and protecting device into operation.

4. A metal-clad isolator switch as claimed in claim 3, in which three current transformers are provided, of which each one is operatively coupled with one of said conductors, and two summation transformers forming part of said control-circuit are provided, each summation transformer being provided with two primary windings and one secondary winding, the one primary winding of said summation transformers being connected in series and fed by the current transformer coupled with the conductor interconnecting the movable switching contacts, the other primary winding of one summation transformer being fed by the current transformer coupled with the conductor extending between earth and the envelope portion surrounding the switching chamber, in which the earth-switch is accommodated and being coupled in counterconnection with the first mentioned primary winding of said summation transformer, the other primary winding of the other summation transformer being fed by the current trans former, coupled with the conductor extending between earth and the envelope portion surrounding the other switching chamber and being coupled in concurrent connection with the first mentioned primary winding of said other summation transformer, and in which a composite signalling and protecting system is provided which has one inoperative and two operative states, the secondary windings of the summation transformers being connected in counterconnection to said composite signalling and protecting system.

5. A double interruption isolator switch and fault indicating means for high voltage electrical systems comprising, in combination;

metal envelope means having portions electrically insulated from each other and defining separate first and second compartments;

a pair of fixed contacts disposed in series in the high voltage electrical system to permit the double interruption thereof, one of said fixed contacts being disposed in said first compartment and the other of said fixed contacts being disposed in said second compartment;

a pair of movable contacts and first conductor means electrically connecting said movable contacts, one of said movable contacts being movable between a normal position engaging said one fixed contact and an interrupting position eiectrically connected to that portion of the envelope means defining said first compartment, the other of said movable contacts being movable between a normal position engaging the other of said fixed contacts and an interrupting position in which it is electrically connected only to said one movable contact through said first conductor means;

second conductor means connecting that portion of the envelope means defining said first compartment to ground;

third conductor means connecting that portion of the envelope means defining said second compartment to ground; and

means responsive (l) to current flow through said second conductor means for indicating that an electrical fault exists in said first compartment and (2) to current flow either through both said first conductor means and said second conductor means or through said third conductor means for indicating that an electrical fault exists in said second compartment.

6. The isolator switch and fault indicating means as defined in claim 5 wherein the last means includes a first winding inductively coupled with said first conductor means, a second winding inductively coupled with said second conductor means, and a third winding inductively coupled with said third conductor means,

7. The isolator switch and fault indicating means as defined in claim 6 wherein said last means also includes a pair of transformers, each having one primary winding energized by said first winding and a second primary winding, the second primary winding of one transformer being energized by said second winding and the second primary winding of the other transformer being energized by said third winding.

8. The isolator switch and fault indicating means as defined in claim 6 wherein said last means also includes three relays energized respectively by said first, second and third windings.

9. A double interruption isolator switch and fault indicating means for high voltage electrical systems comprising, in combination;

metal envelope means having portions electrically insulated from each other and defining separate first and second compartments;

a pair of fixed contacts disposed in series in the high voltage electrical system to permit the double interruption thereof, one of said fixed contacts being disposed in said first compartment and the other of said fixed contacts being disposed in said second compartment;

a pair of movable contacts and first conductor means electrically connecting said movable contacts, one of said movable contacts being movable between a normal position engaging said one fixed contact and an interrupting position electrically connecting to that portion of the envelope means defining said first compartment, the other of said movable contacts being movable between a normal position engaging the other of said fixed contacts and an interrupting position in which it is electrically connected only to said one movable contact through said first conductor means;

second conductor means connecting that portion of the envelope means defining said first compartment to ground;

third conductor means connecting that portion of the envelope means defining said second compartment to ground;

first current-responsive means having an output in response to current flowing through said first conductor means;

second current-responsive means having an output in response to current flowing through said second conductor means;

third current-responsive means having an output in response to current fhowing through said third conductor means;

a pair of indicating devices; and

means for (l) energizing one of said indicating devices in response to an electrical fault in said first compartment which causes an output from said second current-responsive means and (2) energizing the other of said indicating devices in response to an electrical fault in said second compartment which causes either simultaneous outputs from said first and second current-responsive means or an output from said third current-responsive means.

10 The isolator switch and fault indicating means as defined in claim 5 wherein the last means includes three relays, one of said relays being actuated in response to current flow through said first conductor means, a second of said relays being actuated in response to current flow through said second conductor means, and the third of said relays being actuated in response to current flow through said third conductor means. 

1. A metal-clad isolator switch for high voltage and multiple interruption, comprising a metal envelope which is insulated from earth, a selectively operating signalling and protecting system connected between said envelope and earth, two spaced fixed contacts, two movable switching contacts mounted for cooperation with said fixed contacts in the space left between the latter and being, at least in the closed condition of the isolator switch, electrically conductively interconnected, said fixed contacts and said movable contacts being insulated from the envelope, an insulator attached to the envelope and supporting said movable switching contacts, said insulator dividing the space inside the envelope into two switching chambers, which are separated in a gastight manner by said insulator and each contain a fixed contact and a movable switching contact, means for connecting the movable switching contacts with the envelope, when the isolator switch is in its open condition, the envelope portion surrounding one switching chamber being insulated from the envelope portion surrounding the other switching chamber, a conductor extending between one envelope portion and earth and a conductor extending between the other envelope and earth said conductors operatively coupling said envelope portions and, when the isolator switch is in its open condition, the movable switching contacts with the signalling and protecting system in a selective manner, so that at the event of an earth-connection in the isolator switch the selectively operating signalling and protecting system indicates, in which one of the two switching chambers said earth-connection occurs, two individual earthing-switches, each one thereof cooperating with a movable switching contact to connect the latter with the relative envelope portion, two individual signalling and protecting circuits constituting together the selectively operating signalling and protecting system and an auxiliary switch inserted between the movable switching contacts and being closed to interconnect said switching contacts, when the isolator switch is in its closed condition, and being open to separate the switching contacts, when the isolator switch is in its open condition.
 2. A metal-clad isolator switch as claimed in claim 1, in which the movable switching contacts are in the form of axially movable coaxial switching rods mounted for movement in opposite directions and two insulatedly spaced metal tubular members supported by the insulator are provided, each switching rod extending in and being electrically conductively connected with a tubular member, and in which a slide contact is provided which cooperates with the tubular members and is operated by one of the switching rods, said tubular members and said slide contact constituting together the auxiliary switch.
 3. A metal-clad isolator switch for high voltage and multiple interruption, comprising a metal envelope which is insulated from earth, a selectively operating signalling and protecting system connected between said envelope and earth, two spaced fixed contacts, two movable switching contacts mounted for cooperation with said fixed contacts in the space left between the latter and being, at least in the closed condition of the isolator switch, electrically conductively interconnected, said fixed contacts and said movable contacts being insulated from the envelope, an insulator attached to the envelope and supporting said movable switching contacts, said insulator dividing the space inside the envelope into two switching chambers, which are separated in a gastight manner by said insulator and each contain a fixed contact and a movable switching contact, means for connecting the movable switching contacts with the envelope, when the isolator switch is in its open condition, the envelope portion surrounding one switching chamber being insulated from the envelope portion surrounding the other switching chamber, a conductor extending between one envelope portion and earth and a conductor extending between the other envelope and earth said conductors operatively coupling said envelope portions and, when the isolator switch is in its open condition, the movable switching contacts with the signalling and protecting system in a selective manner, so that at the event of an earth-connection in the isolator switch the selectively operating signalling and protecting system indicates, in which one of the two switching chambers said earth-connection occurs, a conductor extending through the insulator and permanently conductively interconnecting the two movable switching contacts, an earthing-switch cooperating with both switching contacts in one of the two switching chambers only, and a composite control-circuit including three individual input-circuits forming part of said control-circuit and two individual signalling and protecting devices controlled by said control-circuit, the conductor interconnecting the two movable switching contacts, the conductor extending between earth and the envelope portion surrounding the switching chamber in which the earthing-switch is accommodated, and the conductor extending between earth and the envelope portion surrounding the other switching chamber each being operatively coupled with an individual input-circuit, said input-circuit reacting on the current that flows through the relative one of said conductors and said control-circuit bringing, at the event of an earth-connection in one switching chamber, one signalling and protecting device and, at the event of an earth-connection in the other switching chamber, the other signalling and protecting device into operation.
 4. A metal-clad isolator switch as claimed in claim 3, in which three current transformers are provided, of which each one is operatively coupled with one of said conductors, and two summation transformers forming part of said control-circuit are provided, each summation transformer being provided with two primary windings and one secondary winding, the one primary winding of said summation transformers being connected in series and fed by the current transformer coupled with the conductor interconnecting the movable switching contacts, the other primary winding of one summation transformer being fed by the current transformer coupled with the conductor extending between earth and the envelope portion surrounding the switching chamber, in which the earthing-switch is accommodated and being coupled in counterconnection with the first mentioned primary winding of said summation transformer, the other primary winding of the other summation transformer being fed by the current transformer, coupled with the conductor extending between earth and the envelope portion surrounding the other switching chamber and being coupled in concurrent connection with the first mentioned primary Winding of said other summation transformer, and in which a composite signalling and protecting system is provided which has one inoperative and two operative states, the secondary windings of the summation transformers being connected in counterconnection to said composite signalling and protecting system.
 5. A double interruption isolator switch and fault indicating means for high voltage electrical systems comprising, in combination; metal envelope means having portions electrically insulated from each other and defining separate first and second compartments; a pair of fixed contacts disposed in series in the high voltage electrical system to permit the double interruption thereof, one of said fixed contacts being disposed in said first compartment and the other of said fixed contacts being disposed in said second compartment; a pair of movable contacts and first conductor means electrically connecting said movable contacts, one of said movable contacts being movable between a normal position engaging said one fixed contact and an interrupting position electrically connected to that portion of the envelope means defining said first compartment, the other of said movable contacts being movable between a normal position engaging the other of said fixed contacts and an interrupting position in which it is electrically connected only to said one movable contact through said first conductor means; second conductor means connecting that portion of the envelope means defining said first compartment to ground; third conductor means connecting that portion of the envelope means defining said second compartment to ground; and means responsive (1) to current flow through said second conductor means for indicating that an electrical fault exists in said first compartment and (2) to current flow either through both said first conductor means and said second conductor means or through said third conductor means for indicating that an electrical fault exists in said second compartment.
 6. The isolator switch and fault indicating means as defined in claim 5 wherein the last means includes a first winding inductively coupled with said first conductor means, a second winding inductively coupled with said second conductor means, and a third winding inductively coupled with said third conductor means.
 7. The isolator switch and fault indicating means as defined in claim 6 wherein said last means also includes a pair of transformers, each having one primary winding energized by said first winding and a second primary winding, the second primary winding of one transformer being energized by said second winding and the second primary winding of the other transformer being energized by said third winding.
 8. The isolator switch and fault indicating means as defined in claim 6 wherein said last means also includes three relays energized respectively by said first, second and third windings.
 9. A double interruption isolator switch and fault indicating means for high voltage electrical systems comprising, in combination; metal envelope means having portions electrically insulated from each other and defining separate first and second compartments; a pair of fixed contacts disposed in series in the high voltage electrical system to permit the double interruption thereof, one of said fixed contacts being disposed in said first compartment and the other of said fixed contacts being disposed in said second compartment; a pair of movable contacts and first conductor means electrically connecting said movable contacts, one of said movable contacts being movable between a normal position engaging said one fixed contact and an interrupting position electrically connecting to that portion of the envelope means defining said first compartment, the other of said movable contacts being movable between a normal position engaging the other of said fixed contacts and an interrupting position in which it is electrically connected only to saiD one movable contact through said first conductor means; second conductor means connecting that portion of the envelope means defining said first compartment to ground; third conductor means connecting that portion of the envelope means defining said second compartment to ground; first current-responsive means having an output in response to current flowing through said first conductor means; second current-responsive means having an output in response to current flowing through said second conductor means; third current-responsive means having an output in response to current flowing through said third conductor means; a pair of indicating devices; and means for (1) energizing one of said indicating devices in response to an electrical fault in said first compartment which causes an output from said second current-responsive means and (2) energizing the other of said indicating devices in response to an electrical fault in said second compartment which causes either simultaneous outputs from said first and second current-responsive means or an output from said third current-responsive means.
 10. The isolator switch and fault indicating means as defined in claim 5 wherein the last means includes three relays, one of said relays being actuated in response to current flow through said first conductor means, a second of said relays being actuated in response to current flow through said second conductor means, and the third of said relays being actuated in response to current flow through said third conductor means. 